Fluororesin aqueous dispersion compositions comprise an aqueous dispersion of a fluororesin and further contain one or more additives, such as pigments and fillers, according to the intended use thereof. They are used in providing coated materials obtained through a step of coating such as impregnation coating, dip coating or spray coating and, further, in a large number of application fields such as cast films, plastics additives, fibers, and soil conditioners.
Fluororesin aqueous dispersion compositions comprising tetrafluoroethylene copolymers [TFE copolymers], such as tetrafluoroethylene/perfluoro(alkylvinylether) copolymers [PFAs], and polytetrafluoroethylene [PTFE] have so far been prepared by using alkylphenol-derived nonionic surfactants as dispersants (alkylphenol-based dispersants).
However, since alkylphenols are suspected of endocrine disrupters (environmental hormones), the development of the alkylphenol type dispersants not generating any endocrine disrupters has been awaited.
PTFE-based aqueous dispersions are known in which aliphatic polyoxyalkylene ethers represented by the formula R1-O-A1-H (in which R1 represents a straight or branched or cyclic, saturated or unsaturated aliphatic hydrocarbon group containing 8 to 24 carbon atoms and A1 represents a polyoxyalkylene chain having 2 to 50 oxyethylene groups and 0 to 30 oxypropylene groups) are used as dispersants that will not generate any endocrine disruptors (cf. e.g. Japanese Kokai Publication Sho-47-6538, pages 1-4).
The aliphatic polyoxyalkylene ethers to be used in PTFE-based aqueous dispersions further include those having a cloud point of higher than 45° C. but not higher than 85° C. (e.g. Japanese Kokai Publication Hei-08-269285, pages 1-3), those whose aliphatic hydrocarbon group has one secondary carbon atom in the middle of the principal chain thereof (e.g. Japanese Kokai Publication Hei-11-152385, pages 1-3), those having at least one oxypropylene group per molecule (e.g. Japanese Kokai Publication Hei-11-240993, pages 1-4), and isotridecyl ether-based surfactants comprising an isotridecyl group having at least three branches, together with oxypropylene groups to be used in foam-inhibiting surfactants (e.g. Japanese Kohyo Publication 2000-511578).
As for the process for producing isotridecyl alcohol-derived surfactants, an industrial process generally comprising etherifying oxo alcohols obtained by hydroformylation of olefins containing 12 carbon atoms according to the oxo process is presented in U. Kaluza und K. Taeger: Tenside Surf. Det., vol. 33, paragraph 46 (1996).
The C12 olefins used in this production process are obtained by monomer addition, and the use, as the monomer, of butene(s) alone, propylene alone, or a mixture of butene(s) and propylene is known in the art. According to the examples of Japanese Kohyo Publication 2000-511578, for instance, a mixture of 1-butene and 2-butene is trimerized.
The PTFE-based aqueous dispersions mentioned above are used in the following manner: coated films formed by application thereof to substrates are heated, for baking, to temperatures not lower than the melting point of the fluororesins. However, these PTFE-based aqueous dispersions have problems: they are all poor in film-forming properties and the coat films obtained therefrom are poor in luster.
Those aqueous dispersions prepared by applying such dispersants not generating endocrine disruptors to TFE copolymers such as PFAs or to PTFE species forming a core/shell structure have problems, namely these polymers are highly shrinkable, hence the coating films formed therefrom are readily cracked in the step of baking; further, the film-forming properties of the dispersions and the luster of the coating films formed therefrom are markedly deteriorated.
Among the fluororesin-based coating compositions, there are ones resulting from incorporation of carbon black, graphite or the like as an electrically conductive filler in aqueous dispersion of PTFE or the like so that the coating films obtained may be rendered electrically conductive.
The conductive filler-containing aqueous dispersions have problems, namely they are inferior in coating film leveling and cracking resistance to those not containing conductive filler, their film-forming properties are deteriorated, hence those articles coated therewith cannot be used in those fields of application where tack-freeness and surface smoothness, among others, are required, for example in the field of OA (office automation) equipment and appliances.
A method available for improving the film-forming properties, coating film leveling properties and luster of the fluororesin-based coating compositions in the form of aqueous dispersions comprises adding a film-forming ingredient comprising an acrylic resin or polyoxyethylene-based prepolymer, for instance.
However, the addition of such a film-forming ingredient produces problems in that the composition of the aqueous dispersion becomes complicated and that the film-forming ingredient generates gases in the step of baking of the coatings.
The method comprising adding a film-forming ingredient has a further problem: when at least one of TFE copolymers such as PFAs, PTFE species with a core/shell structure, and conductive fillers is incorporated, either the film-forming properties or the luster of coating films will never be improved.